1. Field of the Invention
The present invention relates to an optical line scanning imaging device, and, in particular, to a filter lens device for an optical scanner for reproducing color images formed on a document, the lens device scanning the entire document for each color being scanned.
2. Description of the Prior Art
U.S. Pat. No. 4,667,253 to Chen discloses an optical linear scanning system which is capable of producing black and white images and which utilizes a pinch roller drive mechanism which drives material to be imaged past a light source. Successive scan line images which may comprise document or picture information are formed into a narrow line image which is directed through a channel to an imaging lens. The image is focused by the lens onto a linear photo-sensitive detector array, which converts the image into electrical signals. These electrical signals may be fed to an appropriate conventional signal processor which placed them in proper form for transmission or for utilization on a local imaging device. The commencement of the scanning is signaled by means of a position detector which mechanically senses when the material to be scanned enters the imaging area and again when it leaves such area, such that the scanning can be properly synchronized. Although this Chen scanning system provides a significant advance over the prior art, it is limited to scanning a black-and-white document.
U.S. Pat. No. 4,809,062 to Chen discloses a system that produces color images by means of a synchronized color wheel having red, green and blue filters placed in the optical scanning path and driven rotatably in synchronization with the scanning operation.
Although the Chen color scanner operates satisfactorily, it has certain disadvantages associated with its use. For example, color scanning is accomplished by rotating the turning wheel, the optical scanning device continually and successively (sequentially) scanning red-green-blue lights in turn for each line scanned. Interrupting the document movement for the intermittent scanning will reduce the document scanning resolution. For example, the Chen optical black-and-white scanner has a resolution of up to 300 dots per inch (dpi), the resolution decreasing to 100 dpi after installing the Chen color scanner device. Moreover, it is time-consuming to require a pause for every line scanned and then move the document again only after the line has been scanned three times. In addition, with different transmittance ratios for red, blue and green filters, the data processing technique is very complicated for consecutive scanning of three colors because the photo-sensitive detector array (such as a CCD) will display disparate magnifying ratios after processing different light signals.
Further, the physical size of the scanner device resulting from using the turning wheel and its associated driver and controller limits the commercial viability of the device. In addition, since the Chen color scanner device uses rotation of the turning wheel to scan colored documents, the image-forming components of the device require stringent synchronization with the rotation of the turning wheel in order to obtain accurate scanned images. Although it is not difficult to achieve this kind of synchronous controlling technique with current technologies, the scanning time is increased, which increases system cost and complexity.
What is desired therefore is to provide a filter lens device for optical color scanners which will increase the resolution and speed of scanning while reducing the system size, cost and complexity.